Evaporator and loop heat pipe employing it

ABSTRACT

The disclosure relates to an evaporator and a loop heat pipe employing it. The evaporator includes a shell having an evaporation chamber and a compensation chamber defined therein, a partition being received in the shell and partitioning the evaporation chamber and the compensation chamber, and a wick structure being adhered to an inner wall of the shell corresponding to the evaporation chamber and extending through the partition and into the compensation chamber. The loop heat pipe includes the evaporator mentioned above, a pipe connecting two opposite ends of the evaporator to form a closed loop and a working medium contained in the closed loop.

BACKGROUND

1. Technical Field

The disclosure relates to a heat dissipation device and, more particularly, to an evaporator and a loop heat pipe employing it.

2. Description of Related Art

Loop heat pipes have excellent heat transfer performance due to their low thermal resistance, and are therefore an effective means for transfer or dissipation of heat from heat-generating components such as central processing units (CPUs) of computers.

A conventional loop heat pipe includes an evaporator having a wick structure adhered to an inner wall thereof. The evaporator includes an evaporation chamber and a compensation chamber. A predetermined quantity of bi-phase working medium is contained in the evaporator.

During operation of the loop heat pipe, the wick structure disposed in the evaporation chamber absorbs heat from the CPU. A part of the heat absorbed by the wick structure in the evaporation chamber evaporates the working medium in the evaporation chamber into vapor; another part of the heat is transferred to the wick structure in the compensation chamber and evaporates the working medium in the compensation chamber into vapor. The compensation chamber gets a reverse vapor pressure to make thus an effective vapor pressure of the loop heat pipe increasingly decreased. On the other hand, the wick structure in the compensation chamber has a large amount of air bubbles accreted thereon to reduce a permeation rate of the working medium in the compensation chamber resulting in that the working medium is evaporated out.

What is needed, therefore, is a loop heat pipe which can overcome the above problems.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is an isometric, assembled view of a loop heat pipe in accordance with an embodiment of the disclosure.

FIG. 2 is a sectional, partially exploded view of an evaporator of the loop heat pipe of FIG. 1, together with a part of a pipe connecting two opposite ends of the evaporator.

FIG. 3 is a partially schematic view of an operation principle of the loop heat pipe of FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1, a loop heat pipe in accordance with an embodiment of the disclosure is illustrated. The loop heat pipe comprises an evaporator 10, a pipe 20, and a heat dissipating component 30 thermally engaging with the pipe 20. The pipe 20 interconnects two opposite ends of the evaporator 10 to form a closed loop. A predetermined quantity of bi-phase working medium (see FIG. 3) is contained in the closed loop. In this illustrated embodiment, the heat dissipating component 30 consists of a plurality of parallel spaced fins 32 coiled around the pipe 20.

Referring to FIGS. 2-3, the evaporator 10 is columnar in this embodiment. The evaporator 10 comprises a first tube 11 having an evaporation chamber 14 defined therein and a second tube 13 having a compensation chamber 16 defined therein and engaging with the first tube 11. The first tube 11 has a partition 12 extending from a right end thereof and separating the evaporation chamber 14 from the compensation chamber 16. In an alternative embodiment, the first tube 11 and the second tube 13 can be an integrative hollow shell having a space defined therein and disposing the partition 12 therein which divides the space into the evaporation chamber 14 and the compensation chamber 16. In this embodiment, a wick structure 18 is adhered to an inner surface of the first tube 11 and extends through the partition 12 and into the compensation chamber 16. A length of the evaporation chamber 14 in an axial direction thereof is larger than that of the compensation chamber 16. An outer surface of the first tube 11 is thermally connected with a heat generating electronic component such as a CPU (not shown).

The first tube 11 comprises a first circumferential wall 110, a first sidewall 111 and the partition 12 extending inwards perpendicularly from two opposite ends of the first circumferential wall 110, respectively. The first circumferential wall 110, the first sidewall 111 and the partition 12 cooperatively define the evaporation chamber 14. The first sidewall 111 and the partition 12 define a through hole (not labeled) in a center thereof, respectively. The right end of the first circumferential wall 110 has an annular outer groove 112 defined in an outer surface thereof corresponding to an edge of the partition 12.

The second tube 13 comprises a second circumferential wall 130 and a second sidewall 131 extending inwards perpendicularly from a right end of the second circumferential wall 130. A left end of the second circumferential wall 130 has an annular inner groove 132 defined in an inner surface thereof to form an insert 133. The insert 133 is inserted into the outer groove 112 of the first circumferential wall 110 to make the first tube 11 and the second tube 13 engaging together, whereby the second tube 13 and the partition 12 cooperatively define the compensation chamber 16. The second sidewall 131 defines a through hole (not labeled) in a center thereof. The pipe 20 has an end extending through the through hole of the first sidewall 111 and into the evaporation chamber 14, and another end extending through the through hole of the second sidewall 131 and into the compensation chamber 16.

The wick structure 18 comprises a disc-like main body 180, a pipe-shaped evaporation portion 182 extending perpendicularly from a left side face of the main body 180 and a cylinder protrusion 184 extending perpendicularly from a right side face of the main body 180. The main body 180 and the evaporation portion 182 are located in the evaporation chamber 14, and the protrusion 184 is located in the compensation chamber 16.

The main body 180 has the right side face adhered to a left side face of the partition 12, and has an outer circumferential face adhered to an inner surface of the first circumferential wall 110. The main body 180 is isolated from the working medium in the compensation chamber 16 by the partition 12 for preventing the working medium from permeating the main body 180 directly. The evaporation portion 182 is adhered to the inner surface of the first circumferential wall 110. A columnar vapor channel 140 is defined in a middle portion of the evaporation portion 182 of the wick structure 18 and communicates with the pipe 20. The cross-sectional area of the vapor channel 140 is larger than that of the pipe 20, whereby a vapor in the vapor channel 140 can flow into the pipe 20 quickly. The protrusion 184 extends through the through hole of the partition 12 and into the compensation chamber 16, and absorbs the working medium into the main body 180 and the evaporation portion 182. The protrusion 184 has an outer surface spaced from an inner surface of the second circumferential wall 130.

The wick structure 18 can, for example, consist of porous structures, such as fine grooves integrally formed at the inner surface of the first circumferential wall 110 and at the left side face of the partition 12 and extending into the compensation chamber 16, screen mesh or fiber inserted into the evaporation chamber 14 and the compensation chamber 16, and held against the first circumferential wall 110, or sintered powders combined to the inner surface of the first circumferential wall 110 and the left side face of the partition 12 using a sintering process and extending into the compensation chamber 16.

The working medium is selected from a liquid which has a low boiling point such as water, methanol, or alcohol. The pipe 20 is made of deformable materials compatible with the working medium, such as aluminum, stainless steel, or copper.

In operation of the loop heat pipe, the working medium in the evaporation chamber 14 absorbs heat from the heat generating electronic component and evaporates into vapor. A positive vapor pressure is generated due to the vaporization of the working medium and propels the vaporized working medium into the pipe 20 and toward the heat dissipating component 30. The vaporized working medium dissipates its heat to the heat dissipating component 30 and condenses to liquid in the pipe 20. The positive vapor pressure still exists since the evaporation chamber 14 supplies the vapor continuously. The positive vapor pressure, therefore, propels the condensed working medium in the pipe 20 into the compensation chamber 16. The condensed working medium is accumulated in the compensation chamber 16 and submerges the protrusion 184 of the wick structure 18. The condensed working medium is absorbed by the wick structure 18 from the protrusion 184 to the main body 180 and the evaporation portion 182, and into the evaporation chamber 14 via a capillary force of the wick structure 18. The condensed working medium then evaporates to vapor thus starting another cycle in the loop heat pipe and continuously absorbing heat from the heat generating electronic component and dissipating the heat to the heat dissipating component 30.

The partition 12 prevents the main body 180 of the wick structure 18 from directly contacting with the working medium in the compensation chamber 16, decreasing a contact area of the wick structure 18 with the working medium in the compensation chamber 16, thereby decreasing a reverse evaporation area of the wick structure 18. A reverse vapor pressure of the compensation chamber 16 is reduced, keeping the positive vapor pressure in a normal range. On the other hand, the protrusion 184 of the wick structure 18 extends into the working medium in the compensation chamber 16. Heat that is transferred to the protrusion 184 is condensed quickly, and air bubbles on the protrusion 184 are decreased to keep a permeation rate of the working medium in the compensation chamber 16 for preventing the working medium in the evaporation chamber 14 from being evaporated out.

It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. An evaporator for a loop heat pipe comprising: a shell having an evaporation chamber and a compensation chamber defined therein, the evaporation chamber being for communicating with an end of a pipe and the compensation chamber being for communicating with another end of the pipe; a partition being received in the shell and partitioning the evaporation chamber and the compensation chamber; and a wick structure adhered to an inner wall of the shell corresponding to the evaporation chamber and extending through the partition and into the compensation chamber.
 2. The evaporator as claimed in claim 1, wherein the shell comprises a first tube having the evaporation chamber, the partition being located at a right end of the first tube.
 3. The evaporator as claimed in claim 2, wherein the wick structure comprises a main body and a protrusion extending from a side of the main body, the main body being received in the evaporation chamber, and the protrusion extending through the partition and into the compensation chamber.
 4. The evaporator as claimed in claim 3, wherein the first tube comprises a first circumferential wall, the partition extending inwards from a right end of the first circumferential wall, the shell further comprising a second tube, the second tube comprising a second circumferential wall having a left end thereof engaging with the right end of the first circumferential wall of the first tube by means of an inserting connection.
 5. The evaporator as claimed in claim 4, wherein the right end of the first circumferential wall of the first tube has an outer groove defined in an outer surface thereof corresponding to the partition, the left end of the second circumferential wall of the second tube having an inner groove defined in an inner surface thereof to form an insert, the insert being inserted into the outer groove of the first tube to engage the first tube with the second tube.
 6. The evaporator as claimed in claim 4, wherein the wick structure further comprises an evaporation portion extending from the other side of the main body, the evaporation portion being adhered to an inner surface of the first circumferential wall of the first tube.
 7. The evaporator as claimed in claim 6, wherein the main body of the wick structure has an outer circumferential face adhered to the inner surface of the first circumferential wall of the first tube and has a right side face adhered to a left side face of the partition of the first tube.
 8. The evaporator as claimed in claim 4, wherein the protrusion of the wick structure has an outer surface spaced from an inner surface of the second circumferential wall of the second tube.
 9. A loop heat pipe comprising: an evaporator comprising a shell having an evaporation chamber and a compensation chamber defined therein, a partition being received in the shell and partitioning the evaporation chamber and the compensation chamber, and a wick structure being adhered to an inner wall of the shell corresponding to the evaporation chamber and extending through the partition and into the compensation chamber; a pipe connecting two opposite ends of the evaporator to form a closed loop; and a working medium contained in the closed loop.
 10. The loop heat pipe as claimed in claim 9, wherein the shell comprises a first tube having the evaporation chamber, the partition being located at a right end of the first tube.
 11. The loop heat pipe as claimed in claim 10, wherein the wick structure comprises a main body and a protrusion extending from a side of the main body, the main body being received in the evaporation chamber, and the protrusion extending through the partition and into the compensation chamber.
 12. The loop heat pipe as claimed in claim 11, wherein the first tube of the shell comprises a first circumferential wall, the partition extending inwards from a right end of the first circumferential wall, the shell further comprising a second tube, the second tube comprising a second circumferential wall having a left end thereof engaging with the right end of the first circumferential wall by means of an inserting connection.
 13. The loop heat pipe as claimed in claim 12, wherein the right end of the first circumferential wall of the first tube of the shell has an outer groove defined in an outer surface thereof corresponding to the partition of the shell, the left end of the second circumferential wall of the second tube having an inner groove defined in an inner surface thereof to form an insert, the insert being inserted into the outer groove of the first tube to engage the first tube with the second tube.
 14. The loop heat pipe as claimed in claim 12, wherein the wick structure further comprises an evaporation portion extending from the other side of the main body, the evaporation portion being adhered to an inner surface of the first circumferential wall of the first tube of the shell and defining a vapor channel in a middle portion thereof communicating with the pipe.
 15. The loop heat pipe as claimed in claim 14, wherein the main body of the wick structure has an outer circumferential face adhered to the inner surface of the first circumferential wall of the first tube of the shell and has a right side face adhered to a left side face of the partition of the first tube.
 16. The loop heat pipe as claimed in claim 12, wherein the protrusion of the wick structure has an outer surface spaced from an inner surface of the second circumferential wall of the second tube of the shell.
 17. The loop heat pipe as claimed in claim 9 further comprising a heat dissipating component mounted on the pipe.
 18. The loop heat pipe as claimed in claim 17, wherein the heat dissipating component comprises a plurality of fins coiled around the pipe. 